An electrophoretic display (EPD) is a non-emissive device based on the electrophoresis phenomenon influencing charged pigment particles dispersed in a dielectric solvent. An EPD typically comprises a pair of spaced-apart plate-like electrodes. At least one of the electrode plates, typically on the viewing side, is transparent. An electrophoretic fluid composed of a dielectric solvent with charged pigment particles dispersed therein is enclosed between the two electrode plates.
An electrophoretic fluid may have one type of charged pigment particles dispersed in a solvent or solvent mixture of a contrasting color. In this case, when a voltage difference is imposed between the two electrode plates, the pigment particles migrate by attraction to the plate of polarity opposite that of the pigment particles. Thus, the color showing at the transparent plate may be either the color of the solvent or the color of the pigment particles. Reversal of plate polarity will cause the particles to migrate back to the opposite plate, thereby reversing the color.
Alternatively, an electrophoretic fluid may have two types of pigment particles of contrasting colors and carrying opposite charges, and the two types of pigment particles may be dispersed in a clear solvent or solvent mixture. In this case, when a voltage difference is imposed between the two electrode plates, the two types of pigment particles would move to the opposite ends. Thus one of the colors of the two types of the pigment particles would be seen at the viewing side.
An electrophoretic display typically exhibits bistability, which means that after charged particles in an electrophoretic fluid are driven to desired locations under an electric field, the charged particles would remain substantially unmoved after the electric field is turned off. In other words, when an image is displayed by driving charged particles to the intended locations, the image would remain unchanged even after the electric field is turned off.